High power microwave and radio frequency networks are used to provide energy for heating, curing, sterilizing, medical imaging, medical therapy, plasma generating, and other processing of substrates or treated medium. The goal for such processing is to optimize the process. This typically means utilizing the least input energy to completely process the maximum process substrate in an efficient manner and controlling the match between the electromagnetic field to such substrate (which may change as the process is carried out). The applications are primarily high power microwave and/or radio frequency energy utilization including the food service industry, medical applications, the heating of manufactured products such as composite material production, the hydrogenation of petroleum products for octane boosting, plasma systems for the electronics industry, and others.
In a typical device, an electromagnetic generator is located on the opposite end of a waveguide from a load. The waveguide itself can have a rectangular, circular, or other cross section, the selection of which is dependent on the system design and desired mode or electromagnetic field map. The tuning mechanism is itself selected in consideration of the waveguide and mode.
Traditionally three, four, or five complete and separate capacitive probes separated by an electrical distance along the transmission line were required. In this traditional approach, for a given reference position on the line, one probe was actuated in order to introduce capacitive reactance, and a second separate probe was needed in order to introduce the other required inductive reactance parameter. This inductive/capacitive reactance control parameter, however, provides only one of the two required in order to obtain a full range of adjustment latitude required in a system using high power radio frequency or microwave processes.
For this reason, in order to implement a complete tuner network, a second and completely independent set of inductive and capacitive adjustments must be included. (This second set of inductive/capacitive elements is identical to the ones previously described herein.)
In prior waveguide devices, for a full range of adjustment, preferably two pair of two probes (four probes in total) are required (rectangular waveguide example in FIG. 6). (While it is possible to have three probe tuner implementations using capacitive probes, these devices cover only three axes and not four, thus compromising overall performance and tuning range.) This traditional probe approach requires four independent capacitive probe drive mechanisms 100, 101, 102, 103. In addition, the four probes must be spaced apart along the line or waveguide in order to allow the tuner to synthesize all four axes. The spacing 105, 106, 107 is a precise 5/8 electrical waveguide wavelength along the tuner. Since there are four probes on this traditional network, the three spaces 105, 106, 107 between the capacitive probes must be tightly controlled to maintain their relative separation. This type of tuner is therefore sensitive to operational changes in frequency, as the 5/8 wavelength spacing is only actually available at a single frequency for a fixed geometry network. This four probe tuner is therefore quite sensitive in initial setup and in subsequent operation. In addition, the successive 5/8 wavelength spacings, as they relate to frequency, are additive increasing the frequency sensitivity. This four probe tuner is also quite lengthy (at least three times the space between adjacent probes each separated substantially equally; i.e., about 34+1/2" in a 915 mHz. device).
Other cross section waveguides have equivalent design and operation limitations.